1. Field of the Invention
The present invention relates to a process for producing a vacuum ultraviolet ray-excited light-emitting phosphor. Particularly, the present invention relates to a process for producing a vacuum ultraviolet ray-excited light-emitting phosphor used in various displays of light emitting type such as a plasma display panel (hereinafter, sometimes abbreviated as “PDP”) and the like, and the phosphorpaste. More particularly, the present invention relates to a process for producing a vacuum ultraviolet ray-excited light-emitting phosphor having excellent life property of brilliance, which is suitable as a material of a fluorescent surface of the display, and the phosphor paste.
2. Description of the Related Art
In cathode-ray tubes and color liquid crystal displays, increase in size of images is difficult, on the other hand, PDP is a flat panel display enabling it, and expected to be used for indication or as a large screen television in public spaces. PDP is a display element constituted by placing a large number of fine discharging spaces (hereinafter, sometimes abbreviated as “display cell”) into matrix form, and wherein a discharge electrode is provided in each display cell and a phosphor is applied on the inner wall of each cell. In a space in each display cell, a rare gas such as He—Xe, Ne—Xe, Ar and the like is filled and by applying voltage on a discharge electrode, discharge occurs in the rare gas and vacuum ultraviolet ray is radiated. The phosphor is excited by this vacuum ultraviolet ray and emits visible ray. Images are displayed by allotting positions of display cells emitting light. By use of phosphors emitting three primary colors, blue, green and red, full color display can be carried out.
Recently, there are intense developments on phosphors for PDP and a rare gas lamp emitting light by utilizing vacuum ultraviolet ray radiated by rare gas discharge and the like. However, a practically used phosphor for a vacuum ultraviolet ray-excited light-emitting device has insufficient life property of light-emitting brilliance.
As a method for improving life property of light-emitting brilliance of a phosphor, namely as a method for suppressing reduction by time of the brilliance of a phosphor when excited by vacuum ultraviolet ray having constant strength, there is suggested a method for protecting the surface of a phosphor from plasma by coating the surface with a film of a metal oxide or with fine particles. For example, JP-A No. 10-195428 discloses a technology to coat the surface of a phosphor particle with a film of a metal oxide or with fine particles, by allowing a metal alkoxide to adhere to the surface of a phosphor particle and by calcining this. However, since a metal alkoxide manifests quick hydrolysis speed and it is difficult to form on the surface of a phosphor particle a metal oxide film having uniform thickness or metal oxide fine particles having uniform particle size, life property of light-emitting brilliance by vacuum ultraviolet ray excitation is not sufficient.